vfio: Fix broken EEH

vfio_eeh_container_op() is the backend that communicates with
host kernel to support EEH functionality in QEMU. However, the
functon should return the value from host kernel instead of 0
unconditionally.

dwg: Specifically the problem occurs for the handful of EEH
sub-operations which can return a non-zero, non-error result.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
[dwg: clarification to commit message]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

(cherry picked from commit d917e88d85)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/vfio/common.c

@@ -1147,7 +1147,7 @@ static int vfio_eeh_container_op(VFIOContainer *container, uint32_t op)
         return -errno;
     }
 
-    return 0;
+    return ret;
 }
 
 static VFIOContainer *vfio_eeh_as_container(AddressSpace *as)